Development of the network architecture of the Canadian MSAT system

N88DEVELOPMENT

OF THE NETWORK

N. GEORGE DAVIES, MSAT Telesat Canada; VICTOR (formerly with Microtel

ARCHITECTURE

OF THE

CANADIAN

25702

MSAT

Project, Telesat Canada; ALIREZA C.M LEUNG, Chinese University of Pacific Research, Canada).

SYSTEM

SHOAMANESH, Hong Kong,

TELESAT CANADA 333 River Road Ottawa, Ontario KIL 8B9 Canada

ABSTRACT This paper provides a description of the present concept for the Canadian Mobile Satellite (MSAT) System and the development of the network architecture which will accommodate the planned family of three categories oE service; namely, a Mobile Radio Service (MRS), a Mobile Telephone Service (MTS), and a Mobile Data Service (MDS). The MSAT L-band and communications terminals

satellite Ku-band services

and

fixed

dispatcher-type MRS, MTS interconnections

will have transponders between base

cross-strapped to provide L-band mobile

stations

gateway stations to the public

supporting supporting telephone

network, data hub stations supporting the MDS, and the network control centre. This paPer briefly discusses the currently perceived centralized architecture with demand assignment multiple access :for the circuit switched MRS, MTS and permanently assigned channels for the packet switched MDS.

INTRODUCTION The technology to provide commercial mobile satellite communications services, and the market need in North America, have been explored for more than ten years. The lack of frequency spectrum to accommodate land mobile satellite communications', which has been a major impediment to the implementation of the service, was finally overcome at WARC 87. Bands of frequencies between 1530 and 1559 MHz and between 1626.5 and 1660.5 MHz were allocated, respectively, for space-to-earth and earth-to-space links for the land mobile satellite service (LMSS) on a primary, shared primary and secondary basis. While frequency accommodate

PRECEDING

the re-use the

PAGE BLANK

allocation

is

not

generous,

that can be provided with anticipated market demand,

NOT

I=ii..MED

155

analyses multi-beam at least

show

that

satellites for the

the can first

generation systems. Operational experience and advances in technology are expected to increase the capacity of the present allocation and to provide evidence to support the allocation of additional spectrum to meet the requirements. Telesat

Canada

satellites, Procurement

anticipates

to be action

launched for the

Shortly thereafter, the systems will be frozen in may proceed. While much technological development, for

an

MSAT

operational

that

very

in the early space segment

soon

1990s, should

the

will begin

design of the basic MSAT communications order that procurement of the ground segment of the work in the past has focussed on this must now be integrated into the design

SERVICES

The Canadian MSAT system will provide services terminals under three main service categories, namely: •

Mobile

Radio

• •

Mobile Mobile

Telephone Service (MTS) Data Service (MDS)

Radio

time used. shared base

The

MTS

telephone portable

L-band

mobile

(MRS)

two-way voice and optional voice-band data base station and user terminals belonging to

network. This service is primarily targeted to meet for voice dispatch operations. The MRS will be a service and subscribers will be charged for the air

The service stations.

Telephone

to

(MRS)

will provide between a

the same private customers' needs circuit switched

Mobile

Service

Service

The MRS communications

of

system.

COMMUNICATIONS

Mobile

design

be determined. in late 1988.

will

Service

is intended

be

provided

through

privately

owned

or

(MT$) to

provide

service (PSTN) mainly and fixed terminals.

an

extension

to mobile The service

of

the

terminals, will be

public

switched

but also to some provided thro&gh a

number of gateway stations interconnected with the PSTN. The service will operate on a circuit-switched basis and subscribers will be charged for air time. Mobile

Data

The capabilities through an packet of

Service

(MDS)

packet-switched

MDS

will

provide

co_nunicati_n

between mobile terminals and a subscriber's MDS data hub station. Subscribers will be charged data transmitted. Most of the MDS applications

supported through Network Control headquarters and

a

Data Centre dispatch

to

the

NCC

office for each will be

Hub

owned by Telesat Canada, located at the (NCC), and interconnected with user centres by means of a Ku-Band VSAT network

or via public packet data networks. If it more data hubs located in other locations. connected

data

through

the

SHF

link

156

or

is by

required, there These data hubs terrestrial

will can

means.

be be

Some applications, such as an Aeronautical Mobile Data service, will require facilities which are compatible with international standards and therefore require their own unique capability. The special purpose data hub could be located at the NCC or at the location of the service provider. The MDS will communications, -

Interactive

--

%Tc=h4

,.,1=*

be

The

of

bearer

and

value-added

data

Digital

Messaging

- Data

Collection

- Bulk

Data

1"%4 o,-.a.e-,.-.l",/T,'_.-J,,-';,-,,.,

- Paging - Data Acquisition POTENTIAL

capable

including:

MARKET

and

FOR

potential

MSAT

Control

Transfer

(Data / Image/Text)

SERVICES

market,

or

need,

for

MSAT

services

in

Canada

is

presently (1986) estimated at 660,000 mobile units, growing to close to a million units by the year 2000. Ninety-two percent of the market is for land mobile, 5% for marine and 3% for aeronautical services. The demand for MSAT 80,000 mobile units some service. It is estimated

voice services is anticipated to iO years after the introduction that 75% of MSAT voice terminals

used to provide an MRS and 25% to provide 70% of this demand will be generated by transportation, minerals, services, construction.

grow to of MSAT will be

an MTS. It is expected that six major industry sectors: forestry, government and

The demand for MDS has not yet been investigated as thoroughly that for MRS and MTS but it is expected to exceed that for the MRS MTS terminals.

MSAT

SYSTEM

as and

DESCRIPTION

The communications payload of the geostationary MSAT satellites will be cross-strapped L-Band and Ku-band transponders. These transponders will provide communications paths between mobile terminals, which will operate at L-band in portions of the 1.5 GHz and 1.6 GHz frequency bands (as will be coordinated fixed Ku-band (14/12 GHz or 13/11GHz) earth communications between stations in the system Telesat implement

Canada the

the will

plans

first

to

network also be

control centre supported.

cooperate

generation

by Telesat stations.

with

system

the with

and

Canada) SHF -

the

and SHF

other

SHF

Consortium

to

U.S.

MSS

one

Canadian

and

one

American satellite, each of which will have the capability to provide back-up services to the other country, as well as to provide services to mobile users who move from one country to the other. In the present satellite will have deployable parabolic

baseline design of the Canadian two large (a minimum of 5 m in reflectors which will generate

157

system [i], each diameter) L-Band nine 2.7 ° beams

covering Canada and the United cover Mexico.

States.

Another pair

of beams may

One or more transponders may transmit into each beam, probably in specific sub-bands of the L-band allocations, as coordinated for each beam. There will be re-use of frequencies in beamsthat are separated by at least two beamwidths, The nominal channel spacing will be 5 kHz for both voice and data signals. Someservices may require a multiple or one half of a basic channel. Initial planning is to have paired L-band downlink (forward) and uplink (reverse) 5 kHz channels. However, the number of reverse channels may not be so severely limited as the forward channels. Within an overall bandwidth limit, it may be possible to associate more than one return channel with an L-band downlink channel and thereby improve particularly for The

SHF

the message handling the MDS and perhaps for the

transponder

will

operate

with

capability signalling an

of channels, channels.

antenna

that

provides

coverage of North America. As there are far fewer design constraints on the SHF links, there is considerable flexibility in the implementation of the back-haul links to the base, gateway and the NCC. Demand assignment multiple employed to provide MRS and MTS satellite channel. Over 60,000 served

by

the

Canadian

satellite

access voice voice in

the

(DAMA) techniques will be subscribers with access to a terminals in Canada can be first

generation

system.

The capacity of the satellite system, expressed as the number of mobile subscribers that can be offered service, is determined through the application of statistical utilization factors (e.g. a 40% activity factor for a voice conversation) and estimate of the traffic generated by an average subscriber. Studies have indicated that the average MRS voice subscriber will use a channel for approximately 150 minutes/month (the average busy hour traffic is 0.0106 erlang). The tolerable probability of all channels being busy, the probability of a call blockage, has been assumed to be 15 percent. Under these conditions, for the initial system, an average of approximately 95 voice users can share each 5 kHz channel. Packet

switching

techniques

will

be

used

to

provide

data

transmission services. It is anticipated that 2,000 - 5,000, perhaps somewhat more, MDS subscribers can be accommodated within a 5 kHz channel. The number of subscribers that can be accommodated will depend packet multiple capacity The

upon the switched

particular user links. The MDS

access (PAMA) for certain data allocation

of

application will likely

and implementation use permanently

channels with the capability applications with DAMA channels. PAMA

channels

for

the

MDS

will

to

of the assigned augment

reduce

the

capacity available for the MRS and MTS services. At any one time, there will be an optimum balance between the capacities allocated for the respective services (optimization based on maximizing revenue, service capacity, or other criteria).

158

The signalling provide

for

to communicate the DAMAcontrol

requests

to

access

the

network

specific DAMA signalling channels Mobile terminals will use L-band request capacity and to receive used for communications. channels will be used to base,

gateway

and

will

within each DAMA access instructions

Correspondingly, communicate DAMA

possibly

the

data

hub

be

functions implemented

and to through

satellite antenna beam. signalling channels to on the channels to be SHF control

DAMA signalling functions to the

stations.

The use of the SHF bands and North American coverage for back-haul to the NCC, base, gateway and data hub earth stations economizes on the use of scarce L-Band frequencies, and provides for economical assignment of channel capacity from one location (rather than from within each beam). In addition, it allows access by a mobile terminal in any beam to any designated base, gateway or data hub station in the system, permits monitoring and control of L-Band access to the system and allows precise control of the signal levels transmitted via the L-Band transponders to the mobile terminals.

for

Studies have indicated that there mobile-to-mobile communications.

double-hopped

MSAT

through

the

Network

is a Such

Control

very limited communications

requirement will be

Centre.

NETWORK ARCHITECTURE

Figure architecture. Station Control

I

illustrates The network

the concept is controlled

(CCS) which embodies the Centre (NCC) to manage

Spacecraft

Control

Figure

i:

Centre

MSAT

(SCC)

Network

for from

the one

MSAT Central

coordinated functions of a the communications network,

to manage

Architecture

159

the

satellite.

and

Interconnections

network Control Network and a

The NCCmaintains control of the communications network through DAMAsignalling channels which use SHF- SHFlinks to interconnect the NCCwith the SHFbase, gateway and data hub stations and SHF- L-band links to interconnect the NCC with the mobile terminals. The signalling controls the allocation of L-band - SHF communications links between the mobile terminals and designated base, gateway and data hub stations. The NCCincorporates a Network ManagementSystem (NMS) and a DAMA Control System (DCS). The major functions of these two systems in the managementof all aspects of the communications network are as follows: Network

[]

Management

System

Network Operation - Initialization and re-initialization of the network - Generation of call routing algorithms - Maintenance of a database of logged-on subscribers - Optimum transponder partitioning - Management of resources to meet

[]

priority

objectives

Network Monitoring and Maintenance - Monitor power levels of transponder access - Gather alarms, monitor and control activation network elements - Report on network status and - Run network diagnostic tests

U

- Control - Generate Dh_IA

of

redundant

performance

Network Administration - Collect call records - Compile traffic, statistics

|

service

Control Call

security billing

network

performance

of subscriber records

and

history

maintenance

access

System

Processing

(Call

Handling)

- Respond to call requests, assign resources and set up if possible, or otherwise signal calling party and take - Inform subscribers of the status of the network - Generate alarms for unusual conditions

m

Call

the call, down call

Administration

- Manage orderly subscriber log-on and log-off - Establish and maintain DAMA assignment and request each beam of the system - Respond to individual terminal status reporting - Record call data - Generate - Command of NMS

polls of network changes to mobile

- Monitor

emergency

elements terminal

channels

160

transmit

power

channels

under

in

control

The

other

elements

of

the

- L-Band mobile and - SHF Base Stations - SHF

Gateway

- SHF Data discussed - the The

network

transportable which support

Stations

which

Hub Stations earlier, and

signalling protocols

architecture terminals the MRS

support

which

are:

the

support

MTS the

MDS,

which

will

be

have

been

channels and

access

techniques

that

u_=d

on

the

signalling channels are a critical aspect of the network architecture. A number of protocols have been explored [2]. Considerable simulation and testing will be required to confirm the performance and ensure that all the problems have been addressed and overcome. The performance of the whole MSAT system will depend upon the performance of these signalling channels.

SUMMARY Telesat

Canada

Consortium order to throughout production

anticipates

cooperating

closely

with

the

U.S.

MSS

to develop a connnon system concept and architecture in reap the benefits of providing a "standard" service North America. This approach will result in large scale of lower cost units built to a common functional

specification. Action during the next year will determine whether the system will be a common coordinated design, perhaps along the lines described in this report, or be a more fragmented collection of services.

must to

More investigative, be done to improve optimize

the

technical

analytical, simulation, and experimental the understanding of the user requirements approaches

and

the

system

work and

design.

Very little of the hardware or software necessary for the implementation of a mobile satellite system exists as a manufactured product at this time. For this reason, the design, specification and procurement of the first generation MSAT system to serve over I00,000 mobiles in Canada and over three times that number in the United States will challenge the technical Canadian and U.S. organizations.

and

management

capabilities

of

the

REFERENCES [i]

Bertenyi, Satellite Federation,

[2]

Razi,

M.,

Multiple Satellite

E.,

and

Wachira,

M.

System, 38th Congress Brighton, U.K. Shoamanesh,

A.,

of

and

Access Schemes Eor Conference, Pasadena,

1987. the

Azarbar, the MSAT U.S.A.

161

Telesat

Canada's

International

B.

1988.

System

s

Mobile

Astronautical

L-Band NASA

JPL

and

SHF

Mobile